We propose to identify mononuclear cells (i.e., T and B lymphocytes and mononuclear phagocytes) in inflammatory infiltrates generated by immunologic mechanisms. We will study the rejection of transplanted tumor cells (hepatoma), autoimmune disease (thyroiditis) and two prototype reactions of cell-mediated immunity, namely delayed hypersensitivity and cutaneous basophil hypersensitivity reactions. We will attempt to study the cells in tissue sections directly by identifying lymphocyte and monocyte cell surface markers and also to obtain the infiltrating cells in suspension for similar studies, by teasing them from the reactions. We will also determine the propensity of purified subpopulations of lymphocytes to emigrate into these various reactions. These studies should help clarify the identity of cells participating in cell-mediated reactions in vivo. Other studies will be aimed at assessing the capacity of lymphocyte subpopulations to initiate cell-mediated reactions in vivo, following transfer into normal or irradiated recipients.